Greenville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenville clear sky chart from 2005-11-06 to 2026-10-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 6% 2 7% 5% 4 5% 4 6% 8% 41%	148220
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 43%	143834
Transparency	Day	40% 5% 12% 21% 17% 5%	151820
	Night	39% 5% 11% 20% 19% 6%	148305
Seeing	Day	16% 8% 23% 25% 19% 9%	18033
	Night	16% 6% 24% 35% 17% 2	27890

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 6% 2 6% 3 3 3 2 4 5% 55%	5258
	11th to 20th	Day	14% 5% 2 5% 3 3 3 2 3 4 58%	5280
	21st to end	Day	14% 10% 3 8% 4 4 4 3 4 5% 41%	5780
February	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 6% 44%	1890
	11th to 20th	Day	20% 7% 2 6% 4 3 4 2 4 5% 45%	1969
	21st to end	Day	16% 6% 3 6% 4 4 4 3 6% 6% 41%	1760
March	1st to 10th	Day	20% 8% 2 6% 3 4 4 4 5% 6% 39%	5045
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 4 6% 54%	5090
	21st to end	Day	13% 5% 2 5% 3 3 4 3 5% 5% 51%	5619
April	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 4 3 6% 8% 52%	2494
	21st to end	Day	10% 4 3 6% 5% 4 4 4 6% 7% 49%	2520
May	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 4 7% 9% 37%	7077
	11th to 20th	Day	13% 7% 2 7% 4 4 4 4 5% 8% 41%	7626
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 6% 9% 37%	8629
June	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 6% 10% 39%	2940
	11th to 20th	Day	9% 4 2 5% 5% 5% 6% 5% 7% 10% 42%	2940
	21st to end	Day	7% 4 2 6% 5% 5% 7% 5% 8% 12% 38%	2910
July	1st to 10th	Day	6% 5% 2 8% 6% 6% 7% 6% 9% 12% 34%	7680
	11th to 20th	Day	10% 7% 3 9% 6% 6% 6% 5% 8% 12% 29%	7680
	21st to end	Day	11% 7% 3 8% 6% 5% 6% 5% 8% 10% 30%	8340
August	1st to 10th	Day	16% 9% 4 9% 6% 6% 6% 5% 8% 11% 19%	6014
	11th to 20th	Day	7% 6% 2 7% 5% 5% 6% 5% 8% 12% 36%	5513
	21st to end	Day	8% 7% 2 7% 4 5% 6% 4 6% 10% 39%	6080
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 8% 41%	2520
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 3 6% 7% 40%	2520
	21st to end	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 35%	2200
October	1st to 10th	Day	14% 6% 2 5% 3 5% 4 2 4 7% 47%	2100
	11th to 20th	Day	13% 6% 2 4 3 3 4 3 4 5% 54%	2100
	21st to end	Day	12% 5% 2 6% 3 3 3 2 4 5% 55%	2280
November	1st to 10th	Day	14% 5% 1 5% 4 3 4 3 4 6% 51%	2057
	11th to 20th	Day	14% 6% 1 5% 3 3 4 3 5% 5% 51%	1963
	21st to end	Day	13% 5% 2 4 3 3 3 3 5% 7% 52%	1811
December	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 5% 5% 52%	2680
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 5% 5% 44%	3070
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 7% 47%	4265
January	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 7% 52%	7635
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 4 55%	7680
	21st to end	Night	16% 8% 3 7% 4 4 3 3 4 5% 44%	8401
February	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 5% 7% 44%	2730
	11th to 20th	Night	19% 8% 3 6% 4 3 3 4 4 6% 41%	2535
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 5% 47%	2043
March	1st to 10th	Night	19% 8% 3 6% 4 3 4 3 4 5% 41%	5028
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 7% 51%	5090
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 6% 50%	5553
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 6% 7% 48%	2100
	11th to 20th	Night	10% 5% 2 5% 4 4 3 4 5% 8% 50%	2075
	21st to end	Night	10% 5% 2 5% 3 4 3 4 6% 8% 50%	2100
May	1st to 10th	Night	10% 8% 3 8% 5% 6% 6% 4 6% 9% 36%	5819
	11th to 20th	Night	14% 6% 3 6% 4 5% 4 3 5% 7% 43%	5234
	21st to end	Night	15% 8% 3 7% 5% 4 5% 4 6% 9% 33%	5505
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 5% 9% 10% 41%	1680
	11th to 20th	Night	9% 6% 2 7% 5% 6% 6% 5% 7% 10% 37%	1680
	21st to end	Night	7% 5% 2 7% 5% 5% 4 6% 8% 12% 39%	1702
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 5% 8% 13% 37%	5278
	11th to 20th	Night	11% 7% 3 8% 6% 5% 6% 5% 9% 11% 27%	5277
	21st to end	Night	14% 8% 3 9% 5% 5% 6% 5% 7% 9% 28%	5736
August	1st to 10th	Night	14% 9% 3 9% 5% 5% 6% 4 7% 10% 27%	4135
	11th to 20th	Night	8% 7% 4 8% 6% 5% 6% 5% 8% 11% 32%	4484
	21st to end	Night	8% 6% 3 7% 5% 6% 6% 5% 8% 9% 38%	5045
September	1st to 10th	Night	9% 4 2 7% 5% 5% 4 4 6% 9% 44%	2100
	11th to 20th	Night	14% 7% 3 7% 4 3 4 4 4 8% 42%	2100
	21st to end	Night	19% 7% 4 8% 5% 4 5% 4 5% 6% 34%	2414
October	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 49%	2520
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 5% 54%	2520
	21st to end	Night	11% 4 2 5% 4 3 3 3 4 5% 57%	2737
November	1st to 10th	Night	14% 6% 2 4 4 3 4 3 4 5% 52%	2461
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 5% 50%	2653
	21st to end	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2804
December	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 4 6% 54%	4720
	11th to 20th	Night	16% 7% 3 7% 4 4 4 3 5% 6% 40%	5345
	21st to end	Night	12% 5% 2 5% 3 3 3 3 5% 7% 50%	6915

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	34% 2 9% 22% 25% 7%	5259
	11th to 20th	Day	34% 2 3 13% 36% 12%	5280
	21st to end	Day	47% 2 5% 18% 18% 9%	5780
February	1st to 10th	Day	42% 3 10% 21% 20% 5%	1890
	11th to 20th	Day	45% 2 6% 18% 22% 5%	1978
	21st to end	Day	44% 4 8% 19% 19% 5%	1760
March	1st to 10th	Day	47% 2 8% 16% 18% 9%	5045
	11th to 20th	Day	33% 2 7% 18% 25% 15%	5090
	21st to end	Day	36% 4 10% 23% 22% 6%	5619
April	1st to 10th	Day	32% 4 10% 24% 24% 7%	2520
	11th to 20th	Day	31% 4 12% 24% 22% 6%	2494
	21st to end	Day	34% 4 13% 25% 20% 3	2520
May	1st to 10th	Day	43% 5% 17% 22% 11% 2	7109
	11th to 20th	Day	42% 4 13% 25% 16% 1	7630
	21st to end	Day	43% 6% 11% 23% 14% 2	8644
June	1st to 10th	Day	39% 6% 14% 21% 18% 2	2940
	11th to 20th	Day	36% 7% 17% 25% 14% 2	2940
	21st to end	Day	35% 9% 18% 24% 13% 2	2910
July	1st to 10th	Day	39% 9% 18% 26% 8% 1	7615
	11th to 20th	Day	46% 11% 21% 16% 5% 1	7611
	21st to end	Day	45% 8% 16% 19% 11%	8156
August	1st to 10th	Day	56% 9% 21% 10% 3	6001
	11th to 20th	Day	37% 8% 20% 26% 8%	5549
	21st to end	Day	39% 6% 13% 29% 12% 1	6080
September	1st to 10th	Day	38% 8% 14% 20% 18% 2	2520
	11th to 20th	Day	42% 6% 11% 21% 19% 3	2520
	21st to end	Day	48% 5% 10% 21% 14% 3	2200
October	1st to 10th	Day	33% 4 9% 24% 25% 5%	3360
	11th to 20th	Day	24% 2 4 20% 28% 22%	3340
	21st to end	Day	26% 2 5% 24% 29% 14%	3618
November	1st to 10th	Day	36% 3 7% 21% 27% 6%	2057
	11th to 20th	Day	36% 3 8% 22% 24% 8%	1963
	21st to end	Day	34% 3 7% 26% 24% 6%	1811
December	1st to 10th	Day	35% 3 8% 23% 24% 7%	2680
	11th to 20th	Day	42% 4 10% 20% 17% 6%	3066
	21st to end	Day	38% 3 11% 26% 21% 2	4265
January	1st to 10th	Night	33% 3 11% 21% 26% 7%	7636
	11th to 20th	Night	34% 3 4 15% 33% 11%	7680
	21st to end	Night	45% 2 5% 18% 22% 8%	8401
February	1st to 10th	Night	42% 3 8% 21% 20% 6%	2730
	11th to 20th	Night	45% 3 9% 17% 20% 7%	2537
	21st to end	Night	39% 3 8% 21% 21% 8%	2043
March	1st to 10th	Night	46% 3 8% 14% 20% 9%	5028
	11th to 20th	Night	34% 4 9% 14% 23% 16%	5090
	21st to end	Night	36% 3 9% 26% 20% 6%	5553
April	1st to 10th	Night	35% 5% 10% 20% 23% 7%	2100
	11th to 20th	Night	33% 4 11% 25% 21% 6%	2075
	21st to end	Night	33% 4 13% 28% 18% 4	2100
May	1st to 10th	Night	45% 5% 17% 21% 11% 1	5849
	11th to 20th	Night	42% 5% 11% 25% 16% 1	5235
	21st to end	Night	48% 7% 13% 21% 11% 1	5513
June	1st to 10th	Night	35% 8% 17% 21% 16% 3	1680
	11th to 20th	Night	39% 8% 16% 22% 12% 2	1680
	21st to end	Night	36% 9% 18% 24% 12% 1	1702
July	1st to 10th	Night	37% 10% 21% 23% 8% 1	5235
	11th to 20th	Night	47% 12% 22% 13% 6%	5226
	21st to end	Night	50% 8% 15% 16% 10% 1	5606
August	1st to 10th	Night	51% 9% 23% 14% 3	4124
	11th to 20th	Night	42% 9% 22% 20% 6%	4514
	21st to end	Night	40% 7% 13% 26% 13% 2	5045
September	1st to 10th	Night	36% 6% 17% 20% 17% 4	2100
	11th to 20th	Night	41% 6% 11% 22% 17% 2	2100
	21st to end	Night	50% 5% 10% 17% 15% 2	2414
October	1st to 10th	Night	38% 4 7% 21% 26% 4	4040
	11th to 20th	Night	24% 3 5% 18% 25% 25%	4019
	21st to end	Night	24% 2 7% 27% 26% 14%	4349
November	1st to 10th	Night	36% 3 6% 22% 28% 5%	2461
	11th to 20th	Night	37% 3 8% 17% 26% 9%	2653
	21st to end	Night	33% 3 8% 24% 25% 6%	2804
December	1st to 10th	Night	34% 2 8% 16% 30% 10%	4720
	11th to 20th	Night	45% 4 11% 15% 18% 7%	5348
	21st to end	Night	34% 4 12% 27% 21% 2	6915

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 20% 38% 15% 5%	330
	11th to 20th	Day	18% 24% 34% 18% 6%	330
	21st to end	Day	21% 18% 40% 16% 4 1	363
February	1st to 10th	Day	18% 13% 44% 20% 5%	330
	11th to 20th	Day	30% 14% 37% 16% 4	457
	21st to end	Day	22% 12% 36% 22% 6% 1	446
March	1st to 10th	Day	19% 14% 33% 27% 6% 1	540
	11th to 20th	Day	19% 18% 34% 21% 8% 1	540
	21st to end	Day	18% 11% 37% 24% 8% 2	594
April	1st to 10th	Day	17% 16% 30% 23% 11% 3	540
	11th to 20th	Day	11% 13% 30% 29% 12% 5%	532
	21st to end	Day	13% 8% 29% 26% 19% 4	540
May	1st to 10th	Day	14% 10% 35% 22% 13% 5%	543
	11th to 20th	Day	17% 4 20% 30% 20% 8%	567
	21st to end	Day	16% 4 18% 27% 21% 15%	617
June	1st to 10th	Day	11% 3 17% 32% 24% 12%	570
	11th to 20th	Day	12% 3 17% 25% 26% 17%	570
	21st to end	Day	9% 2 14% 28% 33% 16%	570
July	1st to 10th	Day	10% 2 6% 25% 37% 20%	565
	11th to 20th	Day	11% 2 5% 28% 34% 20%	564
	21st to end	Day	11% 2 9% 29% 35% 15%	620
August	1st to 10th	Day	16% 4 11% 26% 27% 17%	566
	11th to 20th	Day	13% 2 9% 25% 32% 19%	559
	21st to end	Day	11% 3 11% 27% 26% 23%	627
September	1st to 10th	Day	12% 3 13% 26% 25% 21%	570
	11th to 20th	Day	17% 4 11% 26% 28% 14%	570
	21st to end	Day	23% 2 18% 24% 23% 9%	570
October	1st to 10th	Day	18% 4 17% 24% 25% 12%	570
	11th to 20th	Day	15% 8% 24% 28% 19% 6%	570
	21st to end	Day	15% 6% 25% 27% 21% 7%	615
November	1st to 10th	Day	21% 6% 25% 31% 14% 4	535
	11th to 20th	Day	18% 9% 32% 29% 11% 2	468
	21st to end	Day	17% 11% 26% 26% 18% 2	351
December	1st to 10th	Day	20% 10% 41% 20% 7% 1	220
	11th to 20th	Day	19% 8% 38% 24% 10% 2	220
	21st to end	Day	20% 11% 38% 19% 10% 2	294
January	1st to 10th	Night	19% 12% 36% 27% 6%	840
	11th to 20th	Night	18% 12% 31% 33% 6%	840
	21st to end	Night	19% 9% 39% 30% 4	924
February	1st to 10th	Night	22% 8% 36% 30% 4	840
	11th to 20th	Night	24% 13% 38% 24% 2	823
	21st to end	Night	20% 13% 35% 29% 4	692
March	1st to 10th	Night	17% 10% 35% 32% 6%	840
	11th to 20th	Night	20% 10% 36% 27% 7% 1	840
	21st to end	Night	17% 9% 37% 29% 6%	924
April	1st to 10th	Night	15% 10% 35% 34% 5%	840
	11th to 20th	Night	13% 9% 35% 32% 11% 1	831
	21st to end	Night	13% 6% 31% 41% 9% 1	840
May	1st to 10th	Night	13% 9% 32% 36% 10% 1	839
	11th to 20th	Night	15% 4 22% 41% 16% 1	621
	21st to end	Night	12% 2 16% 40% 29% 1	594
June	1st to 10th	Night	10% 2 18% 48% 20% 1	420
	11th to 20th	Night	11% 3 14% 45% 24% 3	420
	21st to end	Night	7% 3 12% 48% 28% 2	442
July	1st to 10th	Night	9% 2 7% 40% 37% 5%	615
	11th to 20th	Night	11% 1 4 36% 42% 6%	612
	21st to end	Night	8% 2 10% 40% 34% 6%	690
August	1st to 10th	Night	15% 2 6% 40% 34% 4	627
	11th to 20th	Night	13% 2 6% 36% 37% 6%	795
	21st to end	Night	13% 2 8% 32% 38% 6%	924
September	1st to 10th	Night	12% 2 10% 34% 36% 6%	840
	11th to 20th	Night	17% 3 10% 35% 31% 4	840
	21st to end	Night	23% 3 12% 34% 26% 2	840
October	1st to 10th	Night	17% 3 15% 34% 26% 5%	840
	11th to 20th	Night	16% 7% 22% 35% 19% 2	840
	21st to end	Night	14% 4 24% 34% 20% 3	913
November	1st to 10th	Night	17% 5% 21% 38% 16% 3	820
	11th to 20th	Night	18% 8% 25% 35% 12% 1	840
	21st to end	Night	15% 7% 27% 36% 14% 1	840
December	1st to 10th	Night	19% 8% 28% 37% 7%	840
	11th to 20th	Night	18% 7% 27% 39% 9%	840
	21st to end	Night	16% 8% 31% 35% 9%	924

Page generated at 2026-10-26 04:37:50. Version ac07

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